There are known axial air gap rotating electric machines in which a stator and a rotor plane-face each other with a predetermined air gap interposed therebetween in a radial direction of a rotating shaft. In addition to an advantage that the structure becomes thin (flat), the axial air gap rotating electric machine can increase a structural facing area between the stator and the rotator. Therefore, the axial air gap rotating electric machine has a structure suitable for high power density and high efficiency.
As a stator used for such an axial air gap rotating electric machine, there are known structures disclosed in Patent Literature 1 and Patent Literature 2. Patent Literature 1 and Patent Literature 2 disclose an axial air gap rotating electric machine having a configuration in which a plurality of stator members each in which a coil is wound around an outer peripheral side surface of a laminated iron core having a substantially trapezoidal shaped end side surfaces are arranged about a rotating shaft in a ring shape, and are fixed to an inner circumferential surface of a motor housing.
On the other hand, the axial air gap rotating electric machine has the structure suitable for high power density and high efficiency, but has characteristics that a shaft voltage generated in a bearing is increased as the facing area between the stator and the rotor is relatively large. For example, in a permanent magnet rotating electric machine driven by an inverter, a common mode voltage of the inverter causes an electrostatic coupling to the rotor side to generate the shaft voltage. An excessively large shaft voltage causes electrocorrosion of the bearing, thereby reducing the life of the bearing. In the axial air gap rotating electric machine with the large facing area between the stator and the rotor, there is a tendency of easily increasing an electrostatic capacitance between the coil and the rotor. Particularly, the axial air gap rotating electric machine may have a structure in which stator cores are held in a housing by a resin molding to secure the strength, and the like. Thus, the stator cores become floating potential, the electrostatic capacitance between the coil and the rotor is further increased, and the shaft voltage becomes high.
Patent Literature 3 discloses a technology for reducing the shaft voltage of the axial air gap rotating electric machine. Specifically, a stator core member has a configuration in which an end part of an iron core is slightly protruded from an opening portion of a tubular bobbin into which a columnar iron core is inserted. A plate-like conductive member which is in contact with the inner circumferential surface of the housing from a vertical direction and is conductive is brought into contact with the outer peripheral side surface of the protruded (exposed) portion of the iron core, to reduce the electrostatic capacitance between the coil and the rotor.